1. Field of the Invention
The present invention relates to programmed single mode or controlled multimode radiofrequency wave heating of a material. In particular, the present invention relates to methods for determining a dielectric constant of a material as a function of time or for regulated, programmed heating of a material determined by changes of dielectric constant.
2. Prior Art
Many industrial and scientific applications of microwave (300 MHz-30 GHz) energy have emerged during the past 20 to 30 years of research and development. These applications include home and commercial heating and processing of foods, diathermy heating for cancer treatment, the production of plasma sources for plasma processing, plasma chemistry and fusion research, heat treatment of metal and semiconductor surfaces, and curing of polymer and composite materials. As a result of these many years of development, approaches to microwave applicator (or microwave coupler) design are well established. For example, most heating or processing applications make use of either non-resonant applicators in the form of single or multi-pass slotted waveguide, or multimode resonant cavities. However, modern microwave processing applications have imposed new requirements in applicator design for precision heating.
In response to increased interest in energy efficiency and interest in precision control of processing, recent trends in applicator design have centered on improving heating uniformity, increasing applicator coupling efficiency and on the development of electrical feedback control of microwave processing systems. In addition, if one is interested in understanding fundamental electromagnetic/material interactions it is desirable to be able to diagnose the material properties and the electromagnetic field strengths and patterns during the processing cycle. When considering efficiency and diagnosis as design criteria, the single mode (or controlled multimode) cavity applicator appears to have important advantages over multimode applicators.